In QUDV, base quantities and base units are modeled as object properties of SystemOfQuantities and SystemOfUnits (i.e. roles). We distinguish between simple and base kinds of quantity and units: (2474)

A simple kind of quantity or a simple unit does not depend (for its definition) on any other kind of quantity or unit. (2479)

A base kind of quantity is a role that is assigned to selected kinds of quantity in the context of a system of quantities. (247A)

A base unit is a role that is assigned to selected units in the context of a system of units. (2475)

For the SI system of units, this separation of simple and base units e.g. cleanly solves the problem of selecting the PrefixedUnit "kilogram" as a base unit. The "kilogram" is defined through object properties to the Prefix "kilo" and to the SimpleUnit "gram". (2476)

QUDV contains an algorithm written in OCL that precisely specifies how a quantity dimension for a given kind of quantity in a given system of quantities can be derived automatically. (2477)

In the OWL version of QUDV the AffineConversionUnit (conversion unit defined with factor and offset to a reference unit) is removed because this is better handled by a LinearConversionUnit and adding an equivalent property between scale value definitions of different scales. E.g. the offset needed to convert between a thermodynamic temperature in kelvin and a Celsius temperature in degree Celsius can be derived when the triple point of water scale value definitions in both the Kelvin and Celsius scales are declared equivalent. (2478)

The SpecializedQuantityKind is modeled explicitly because QUDV complies with the strict separation into (MOF) meta levels in UML. QUDV is a pure level M0 UML or SysML <<modelLibrary>>. Accordingly in OWL2 DL it is not allowed to use metaclasses (using owl:class). This is also not supported in Protégé v4 (yet). In OWL2 Full it would perhaps be possible to model the kind of quantity / quantity specialization relationships more elegantly. (247B)